Document FR-2,898,284 aims to use a demixing absorbent solution having the property of splitting up when said absorbent solution laden with acid compounds is heated. The absorbent solution is contacted with the gas to be deacidized. During regeneration, the solution divides into two phases: a fraction rich in acid compounds and a fraction poor in acid compounds. Thus, document FR-2,898,284 aims to regenerate by distillation only the fraction that is enriched in acid compounds in order to minimize the energy required for regeneration of the absorbent solution.
However, thermal regeneration of the absorbent solution favours degradation of the organic compounds contained in the absorbent solution. The organic compounds degrade upon passage through the reboiler that provides the thermal energy required for regeneration. It is the part of the process where the operating conditions are the severest. Furthermore, in the case of combustion fumes treatment, for example thermal power plant fumes, the presence of oxygen can generate other degradation reactions. Under these combined effects, organic degradation products and non-regeneratable salts accumulate within the absorbent solution. This accumulation alters the properly of acid gas absorption by the absorbent solution. Besides, the organic degradation products can have a surface-active nature. Thus, they can pose foaming problems, or liquid-liquid separation problems by stabilizing the phases in form of an emulsion. These liquid-liquid separation problems can be encountered when using the method described in document FR-2,898,284 or in the case of gas treatment where the liquid hydrocarbons are eliminated from the absorbent solution by liquid-liquid separation, after the absorption column. Furthermore, non-regeneratable salts are known to be responsible for corrosion and foaming problems within the units.
In order to limit these problems, the absorbent solution is generally purified by ion exchange or by distillation, in a sequential or continuous manner. Within the context of purification through ion exchange, ion-exchange resins are used to replace the non-regeneratable salts by hydrogenocarbonates that are regeneratable. In the case of purification by distillation, the water and the reactive compounds are vaporized and sent back to the capture unit, thus allowing the weakly volatile organic degradation products and the non-regeneratable salts to accumulate in the bottom of the distillation drum. They are thereafter eliminated. Besides, when the reactive compounds are weakly volatile, it may be difficult to vaporize the absorbent solution at atmospheric pressure. The absorbent solution is then subjected to purification by vacuum distillation, which is more expensive than distillation at atmospheric pressure, in order to limit the distillation temperature. Despite this distillation temperature decrease, degradations still may occur during this purification operation. The faster the degradation of the absorbent solution, the higher the frequency of the purification operations to guarantee constant performances of the absorbent solution, and maximum non-regeneratable salt concentration in the solution. These purification operations have a quite significant impact on the operating costs of the unit. Finally, since the purification operations through ion exchange or distillation do not allow to remove all of the organic degradation products, it may be necessary to periodically renew all of the absorbent solution when its performances are too low. The costs associated with the purchase of a new solvent feed and with the elimination of the degraded absorbent solution feed are high.
The present invention aims to optimize the operations performed on the absorbent solution by carrying out separation of the regenerated absorbent solution into two fractions: a fraction enriched in water and a fraction enriched in reactive compounds.